In recent years, needs for improving antifogging properties of a plastic and glass surface have been ever-increasing.
As a method for solving the fogging problem, an antifogging coating material that improves hydrophilicity and water-absorbing property of a hardened layer by adding a reactive surface-active agent to an acrylic oligomer has been proposed (Non-Patent Document 1). Also, by improving surface hydrophilicity, antifouling materials having self cleaning property (antifouling property) which can be achieved by floating out and effectively removing the dirt attached to an outer wall and the like (an outer air hydrophobic material and the like) by rain, water spray and the like are drawing attention (Non-Patent Documents 2 and 3).
As a representative hydrophilic resin, there are many known resins that have a number of hydroxyl groups within a molecule such as polyvinyl alcohol. Since these hydrophilic resins have specific properties depending on their chemical structure, product development is carried out in accordance with their specific properties.
Other reported hydrophilic resins include: polymers obtained by using potassium 3-sulfopropylmethacrylate, sodium 2-acrylamide-2-methylpropane-sulfonate and polyethylene glycol diacrylate as described in Patent Document 1; polymers obtained by using sodium 3-sulfopropylmethacrylate and a long-chain urethane diacrylate (trade name NK Oligo UA-W2A, manufactured by Shin-Nakamura Chemical Co., Ltd.) as described in Patent Document 2; polymers obtained by using 2-sulfoethyl acrylate, tetrahydrofurfuryl acrylate, trimethylolpropane acrylate and spiroglycol urethane diacrylate as described in Patent Document 3; polymers obtained by using 2-sulfoethyl methacrylate and/or a (meth)acrylate containing a phosphate group and an epoxy resin as described in Patent Document 4; polymers obtained by using hydroxyethyl methacrylate, sulfoalkylene (C6 to C10) methacrylate and methylenebisacrylamide as described in Non-Patent Document 4, and the like.
Patent Document 1 describes that an obtained transparent gel is used as a bio-adhesive material, Patent Document 2 describes that an obtained polymer is used as a recording material for an ink jet recording with excellent ink-adsorption, high water resistance and no blocking, and Patent Document 3 describes that an obtained polymer is used as an adhesive agent to firmly adhere a metal hub for an optical information disk drive with a resin substrate. Patent Document 4 describes that a polymer obtained by crosslinking of ethylenic unsaturated bonds and concurrent crosslinking of a sulfonic acid group or a phosphate group with an epoxy group by an ionic reaction can be used as an electroconductive hardening film having excellent properties in mechanical performance, solvent resistance, film formation, adhesiveness, transparency and abrasion resistance.
Non-Patent Document 4 describes, among others, that hydrophilic property (the forward contact angle and the backward contact angle) of slightly crosslinked coating film formed on glass changes with the length of alkylene chain (C6 to C10) of the sulfoalkylene methacrylate monomer used and further with the hydration time.
However, the above-described polymers were not suitably qualified to be used as an antifogging material and an antifouling material, since they either have high solubility in water or adsorb water to easily form gels though not soluble in water, or a surface thereof is too soft and susceptible to scratches or are insufficient in hydrophilicity.
Proposed in Patent Document 6, as a method for producing a hydrophilic article, is a double-layered structure having a hydrophilic structure having a hydrophilic monomer on a crosslinked polymer surface, which is formed by a dual-coating method of coating a crosslinkable monomer composition on a surface of a substrate material, irradiating UV light on it in a controlled manner to form an incompletely polymerized crosslinked polymer, then coating it with a hydrophilic monomer and again irradiating UV light to perform block polymerization or graft polymerization of the hydrophilic monomer on a crosslinked polymer surface.
However, the method described above is not preferable because it is apparently complex and costly and the smoothness of surface is easily damaged as compared with, for instance, a general method for forming a single-layered structure by single coating of a composition composed of a hydrophilic monomer and a crosslinkable monomer followed by their polymerization by UV light irradiation and the like.
The present inventors also proposed a polymer using a hydroxyl group-containing (meth)acrylamide compound as a method for addressing the problems mentioned above (Patent Document 5).
Generally, physical properties required of an antifouling resin for coating include high surface hardness and high hydrophilicity. Physical properties required of an antifogging resin for coating include relatively high surface hardness and higher hydrophilicity than that for antifouling use.
Further developments of the method previously proposed by the present inventors were necessary in order to fully satisfy these requirements and to completely address the problems of “fogging” and “fouling”.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-521140    Patent Document 2: Japanese Patent Laid-Open Publication No. H11-115305    Patent Document 3: Japanese Patent Laid-Open Publication No. H08-325524    Patent Document 4: Japanese Examined Patent Application Publication No. S53-010636    Patent Document 5: International Laid-Open Publication No. WO 2004/058900    Patent Document 6: Japanese Patent Laid-Open Publication No. 2001-98007    Non-Patent Document 1: Toagosei Annual Report, TREND 1999, February, pp 39-44    Non-Patent Document 2: Kobunshi, 44(5), p 307    Non-Patent Document 3: Miraizairyo, 2(1), pp 36-41    Non-Patent Document 4: Journal of Colloid and Interface Science, vol. 110(2), pp 468-476 (1986)